In an existing cellular mobile telecommunication system, in order to enhance the utilization rate of frequency spectrum resources and the capability of the whole system and restrict the transmitting power of a base station in the system within a cell, when a User Equipment (UE) moves from a cell to another cell, signals received by the UE from an original cell inevitably become increasingly weak while the received signals in the cell which the UE is entering are becoming increasingly strong. The UE needs to switch to a new cell to maintain the communication quality of the UE.
Under a Frequency Division Duplexing (FDD) mode, in order to perform switching among different frequencies, switching from FDD to Time Division Duplexing (TDD) or switching among systems, measurement needs to be performed for a target cell of switching. If downlink signals are always occupied in time domain, downlink data needs to be received continuously. For a UE with only one set of transceiver, a mechanism, which is a compressed mode, is needed to be able generate a certain idle time slot in a downlink radio frame.
Downlink compressed mode is used for forming a data transmission “gap” for a period of time by using various techniques in a data frame of an air interface. In this gap, a base station transmits no data, and a UE receives no data. In this way, the UE may perform measurement by using the period of time.
When the downlink compressed mode is used, if an uplink frequency of a UE is being transmitted, and a measured frequency is relatively close to the uplink frequency, then the measured frequency may be interfered by uplink transmitting frequency. In order to ensure measurement accuracy, uplink transmission is also needed to be stopped at the moment. This is the uplink compressed mode.
Generally, the uplink compressed mode applies the following methods: reducing spreading factors by half, punching and performing scheduling by a higher layer etc. The downlink compressed mode may apply the methods above except punching. Since the compressed mode may influence the system performance, receivers of some UEs are capable of receiving signals of a plurality of carrier frequencies gradually, thus measurement may be performed among frequencies and systems without starting the compressed mode.
Downlink secondary carrier frequency measurement of a terminal supports Dual-Carrier HSDPA (DC-HSDPA) function is expressed by an information element of Adjacent Frequency measurements without compressed mode. If the information element is included, then a compressed mode is not needed to be started when a UE is measuring adjacent carrier frequencies. If the information element is not included, then a compressed mode is needed to be started when a UE is measuring adjacent carrier frequencies. At the same time, the downlink secondary carrier frequency measurement of the terminal supports DC-HSDPA function is also expressed by an information element of Inter-band Frequency measurements without compressed mode. If the information element is included, then a compressed mode is not needed to be started when a UE is measuring carrier waves of different frequency bands. If the information element is not included, then a compressed mode is needed to be started when a UE is measuring carrier waves of different frequency bands.
With the development of technologies, the multi-carrier frequency HSDPA technology is expected to be introduced into the existing systems. The technology enables a terminal to receive data on three or four carrier waves by using the HSDPA technology so as to multiply the rate of downlink data. Taking a four-carrier frequency HSDPA (4C-HSDPA) system for example, there are four carrier waves (a primary carrier wave and three secondary carrier waves) on downlink, and a terminal needs to be able to monitor the three secondary carrier waves. If the secondary carrier waves which can be detected by the terminal are less than three, a UE may not be able to change a serving cell timely in some areas covered by the 4C-HSDPA technology, thus causing a call drop easily.
To solve the problem above, in the multi-carrier frequency HSDPA technology, when switching needs to be performed among systems or frequencies, a UE needs to start a compressed mode to perform corresponding switching among systems or frequencies, thus resulting in a relatively low utilization rate of system resources and influencing the system performance.